usb: chipidea: split the driver code into units

Split the driver into the following parts:
  * core  -- resources, register access, capabilities, etc;
  * udc   -- device controller functionality;
  * debug -- logging events.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>